Quantum computers utilize quantum mechanical principles in order to perform calculations and quantum devices to form the processor of the quantum computing device. Quantum mechanical phenomena at work may include the superposition of quantum states (the probabilistic nature of quantum mechanics allowing for multiple states simultaneously). The quantum devices used may include superconducting quantum interference devices (SQUIDs), which have quantum mechanical magnetic states. A SQUID may thus correspond to a quantum bit (qubit) for the quantum computing device. At certain temperatures the SQUID may exist in multiple magnetic states simultaneously, exhibiting the superposition of states mentioned above. The presence of multiple states may allow the quantum computing device to more rapidly perform calculations than a conventional deterministic computer.
Most current quantum computing devices operate at very low temperatures to allow the qubits to retain their superposed states for long enough to perform the desired calculations. Further, the calculation speed may increase as temperature decreases. Thus, the operating temperatures of the relevant portions of the quantum computing device are well under 10 Kelvin.
Conventional quantum computing device magnetic memories contain storage cells that may use Josephson junctions as the storage elements. The storage cells in the conventional quantum computing device memory may be local to the qubits. For example, a fabric of SQUIDs and Josephson junctions may form the processor and memory of the quantum computing device. Although separately addressable, the magnetic memory storage cells may still be physically close to the quantum device corresponding to the qubit. The magnetic memories for quantum computers typically operate at the same very low temperatures at which processing is performed. Although described as storing a qubit, the state actually stored in the magnetic memory is a single state of the quantum device. Stated differently, the quantum device may be measured so that the multiple probabilistic states of a qubit may be collapsed down to a single, deterministic state for storage in the magnetic memory.
Although conventional quantum computing device and their memories may function, as quantum computing devices are developed, additional memories are desired. Such quantum computing device memories may be desired to be capable of fast operation at the very low temperatures used in quantum computing devices. Magnetic devices used by other conventional magnetic memories may not be appropriate for such quantum computing device memories. For example, conventional magnetic tunneling junctions are not typically used in quantum computing device magnetic memories because such devices have too high a resistance at low temperatures, may be too slow to program at low temperatures and may have other issues.
Accordingly, what is needed is a method and system that may provide fast magnetic memories capable of operation at low temperatures such as sub-ten Kelvin temperatures. In some cases, the operational temperature may be desired to be well under one Kelvin. The method and system described herein address such a need.